Perception threshold of locomotor symmetry while walking on a split-belt treadmill in healthy elderly individuals.

Some hemiparetic patients walk asymmetrically. To better understand the mechanisms of this deficiency, the perception of locomotor symmetry was investigated in healthy elderly individuals. 16 participants (6 women, 10 men; M age = 70.9 yr., SD = 4.1) walked on a split-belt treadmill either at a self-selected or imposed gait speed. The speed of the two belts was initially similar (or different) and then gradually differed (or matched), so participants had to detect the point of perceived asymmetry (or symmetry). The results revealed that thresholds occurred when the belt speed ratios were .88 and .85. Initial gait speed did not affect the threshold. The parameter that correlated the most with belt speed asymmetry was stance time of the parameters measured. Future studies will investigate whether stroke affects gait symmetry judgments.

Embodying a self-avatar with a larger leg: its impacts on motor control and dynamic stability.

Several studies have shown that users of immersive virtual reality can feel high levels of embodiment in self-avatars that have different morphological proportions than those of their actual bodies. Deformed and unrealistic morphological modifications are accepted by embodied users, underlying the adaptability of one's mental map of their body (body schema) in response to incoming sensory feedback. Before initiating a motor action, the brain uses the body schema to plan and sequence the necessary movements. Therefore, embodiment in a self-avatar with a different morphology, such as one with deformed proportions, could lead to changes in motor planning and execution. In this study, we aimed to measure the effects on movement planning and execution of embodying a self-avatar with an enlarged lower leg on one side. Thirty participants embodied an avatar without any deformations, and with an enlarged dominant or non-dominant leg, in randomized order. Two different levels of embodiment were induced, using synchronous or asynchronous visuotactile stimuli. In each condition, participants performed a gait initiation task. Their center of mass and center of pressure were measured, and the margin of stability (MoS) was computed from these values. Their perceived level of embodiment was also measured, using a validated questionnaire. Results show no significant changes on the biomechenical variables related to dynamic stability. Embodiment scores decreased with asynchronous stimuli, without impacting the measures related to stability. The body schema may not have been impacted by the larger virtual leg. However, deforming the self-avatar's morphology could have important implications when addressing individuals with impaired physical mobility by subtly influencing action execution during a rehabilitation protocol.

Can a Musculoskeletal Model Adapted to Knee Implant Geometry Improve Prediction of 3D Contact Forces and Moments?

Tibiofemoral contact loads are crucial parameters in the onset and progression of osteoarthrosis. While contact loads are frequently estimated from musculoskeletal models, their customization is often limited to scaling musculoskeletal geometry or adapting muscle lines. Moreover, studies have usually focused on superior-inferior contact force without investigating three-dimensional contact loads. Using experimental data from six patients with instrumented total knee arthroplasty (TKA), this study customized a lower limb musculoskeletal model to consider the positioning and the geometry of the implant at knee level. Static optimization was performed to estimate tibiofemoral contact forces and contact moments as well as musculotendinous forces. Predictions from both a generic and a customized model were compared to the instrumented implant measurements. Both models accurately predict superior-inferior (SI) force and abduction-adduction (AA) moment. Notably, the customization improves prediction of medial-lateral (ML) force and flexion-extension (FE) moments. However, there is subject-dependent variability in the prediction of anterior-posterior (AP) force. The customized models presented here predict loads on all joint axes and in most cases improve prediction. Unexpectedly, this improvement was more limited for patients with more rotated implants, suggesting a need for further model adaptations such as muscle wrapping or redefinition of hip and ankle joint centers and axes.

Seated postural organization during bilateral upper limb symmetric and asymmetric pushing tasks in individuals after stroke compared to healthy controls.

BACKGROUND: Asymmetric weight distribution in sitting has been reported in people after stroke. However, postural strategies used during bilateral symmetric and asymmetric movements performed while seated require more evidence to inform rehabilitation strategies. RESEARCH QUESTIONS: How do symmetric and asymmetric effort levels exerted during upper limb (UL) pushing movements affect seated postural organization parameters (weight bearing (WB) between hands and hemibody sides, and forward trunk displacement) of stroke compared to healthy individuals? How are these parameters associated? METHODS: Using an instrumented exerciser, 19 post-stroke individuals were compared to 17 healthy individuals when executing four bilateral UL pushing movements in a seated position: symmetrical pushing at 30 % and 15 % of their maximal force (MF) and asymmetrical pushing with 15 % of their MF for one UL vs. 30 % of the MF for the other UL and vice versa. Anterior and vertical forces of the push, as well as vertical forces under each foot and thigh were compared between groups, sides and conditions. Forward trunk displacement was compared between groups and conditions. Correlations were used to determine the association between trunk displacement, hands and hemibody vertical forces. RESULTS: Increasing pushing effort caused increased WB on thighs and decreased on WB on feet during the 30 % MF symmetric condition compared to the 15 % MF and asymmetric conditions (p < 0.05). Individuals post-stroke showed WB asymmetry and greater forward trunk displacement when compared to healthy persons (p < 0.05). For both groups, hemibody WB and trunk displacement showed moderate association (r > - 0.5) in the asymmetric condition executed with more resistance on the paretic or non-dominant hand. SIGNIFICANCE: Individuals post-stroke presented a similar WB pattern to that of healthy persons during symmetric and asymmetric bilateral UL movements with greater forward trunk displacement and asymmetry. Increased effort and asymmetric force between both UL had effects on seated postural organization strategy.

Effect of Haptic Training During Manual Wheelchair Propulsion on Shoulder Joint Reaction Moments.

Background: Manual wheelchair propulsion remains a very ineffective means of locomotion in terms of energy cost and mechanical efficiency, as more than half of the forces applied to the pushrim do not contribute to move the wheelchair forward. Manual wheelchair propulsion training using the haptic biofeedback has shown an increase in mechanical efficiency at the handrim level. However, no information is available about the impact of this training on the load at the shoulders. We hypothesized that increasing propulsion mechanical efficiency by 10% during propulsion would not yield clinically significant augmentation of the load sustained at the shoulders. Methods: Eighteen long-term manual wheelchair users with a spinal cord injury propelled a manual wheelchair over a wheelchair simulator offering the haptic biofeedback. Participants were asked to propel without the Haptic Biofeedback (HB) and, thereafter, they were subjected to five training blocks BL1-BL5 of 3 min in a random order with the haptic biofeedback targeting a 10% increase in force effectiveness. The training blocs such as BL1, BL2 BL3, BL4, and BL5 correspond, respectively, to a resistant moment of 5, 10, 15, 20, and 25%. Pushrim kinetics, shoulder joint moments, and forces during the propulsive cycle of wheelchair propulsion were assessed for each condition. Results: The tangential force component increases significantly by 74 and 87%, whereas value for the mechanical effective force increases by 9% between the pretraining and training blocks BL3. The haptic biofeedback resulted in a significant increase of the shoulder moments with 1-7 Nm. Conclusion: Increases in shoulder loads were found for the corresponding training blocks but even though the percentage of the increase seems high, the amplitude of the joint moment remains under the values of wheelchair propulsion found in the literature. The use of the HB simulator is considered here as a safe approach to increase mechanical effectiveness. However, the longitudinal impact of this enhancement remains unknown for the impact on the shoulder joint. Future studies will be focused on this impact in terms of shoulder risk injury during manual wheelchair propulsion.

Bilateral motor coordination during upper limb symmetric pushing movements at two levels of force resistance in healthy and post-stroke individuals.

BACKGROUND: Impairments of the upper limb (UL) are common after a stroke and may affect bilateral coordination. A better understanding of UL bilateral coordination is required for designing innovative rehabilitation strategies. OBJECTIVE: To assess bilateral coordination after stroke using time-distance, velocity and force parameters during an UL bilateral task performed by simultaneously pushing handles on a bilateral exerciser at two levels of force. METHODS: Two groups were included to assess bilateral coordination on a newly designed bimanual exerciser- One group of individuals at least 3 months post-stroke (n = 19) with moderate impairment and one group of healthy individuals (n = 20). Participants performed linear movements by pushing simultaneously with both hands on instrumented handles. The task consisted of two one-minute trials performed in sitting at two levels of participants' maximum force (MF): 30% and 15%, with visual feedback. Time-distance parameters, spatial, velocity and force profiles were compared between groups, between levels of resistance and the first part (0-50%) and entire duration of the pushing cycles (0-100%). RESULTS: The mean pushing time was longer at 30% MF compared to 15% MF in the stroke group. Spatial profiles, represented by hand positions on the rail, revealed that the paretic hand lagged slightly behind throughout the cycle. For velocity, both groups displayed good coordination. It was less coupled at 30% than 15% MF and a trend was observed toward more lag occurrence in the stroke group. Except for lower forces on the paretic side in the stroke group, the shape of the force profiles was similar between groups, sides and levels of resistance. For all parameters, the coordination was good up to 75% of the pushing cycle and decreased toward the end of the cycle. CONCLUSIONS: Individuals after stroke presented with overall spatial and temporal coupling of the UL during bilateral pushing movements. The relay of information at different levels of the nervous system might explain the coordinated pushing movements and might be interesting for training UL coordination.

Dynamic estimation of soft tissue stiffness for use in modeling socket, orthosis or exoskeleton interfaces with lower limb segments.

Modeling the interface between the lower limb segments and a socket, orthosis or exoskeleton is crucial to the design, control, and assessment of such devices. The present study aimed to estimate translational and rotational soft tissue stiffness at the thigh and shank during daily living activities performed by six subjects. Smooth orthogonal decomposition (SOD) was used on skin marker trajectories and fluoroscopy-based knee joint kinematics to compute stiffness coefficients during squatting, sitting and rising from a chair, level walking, and stair descending. On average, for all subjects and for all activities, in the anatomical directions observed, the translational and rotational stiffness coefficients for the shank were, respectively, 1.4 ± 1.99kN/m (median and interquartile range) and 41.5 ± 34.3Nm/deg. The results for the thigh segment were 1.79 ± 2.73kN/m and 30.5 ± 50.4Nm/deg. As previously reported in the literature dealing with the soft tissue artifact - considered as soft tissue deformation in this study - the computed stiffness coefficients were dependent on tasks, subjects, segments, and anatomical directions. The main advantage of SOD over previous methods lies in enabling estimation of a task-dependent 6 × 6 stiffness matrix of the interface between segments and external devices, useful in their modeling and assessment.

Knee loading in OA subjects is correlated to flexion and adduction moments and to contact point locations.

This study evaluated the association of contact point locations with the knee medial and lateral contact force (Fmed, Flat) alterations in OA and healthy subjects. A musculoskeletal model of the lower limb with subject-specific tibiofemoral contact point trajectories was used to estimate the Fmed and Flat in ten healthy and twelve OA subjects during treadmill gait. Regression analyses were performed to evaluate the correlation of the contact point locations, knee adduction moment (KAM), knee flexion moment (KFM), frontal plane alignment, and gait speed with the Fmed and Flat. Medial contact point locations in the medial-lateral direction showed a poor correlation with the Fmed in OA (R2 = 0.13, p = 0.01) and healthy (R2 = 0.24, p = 0.001) subjects. Anterior-posterior location of the contact points also showed a poor correlation with the Fmed of OA subjects (R2 = 0.32, p < 0.001). Across all subjects, KAM and KFM remained the best predictors of the Fmed and Flat, respectively (R2 between 0.62 and 0.69). Results suggest different mechanisms of contact force distribution in OA joints. The variations in the location of the contact points participate partially to explains the Fmed variations in OA subjects together with the KFM and KAM.

Postural organization and inter-limb coordination are altered after stroke when an isometric maximum bilateral pushing effort of the upper limbs is performed.

BACKGROUND: Postural strategies of the trunk and the lower limbs are linked to upper limb motor activities. The objective was to analyze the postural organization at the lower limbs as well as the inter-limb coordination during isometric maximal bilateral pushing of upper limbs. METHODS: Fifteen individuals after stroke and 17 healthy participants were assessed with an instrumented exerciser paired with an instrumented sitting surface while they executed isometric bilateral pushes with the upper limbs. The anteroposterior, vertical and mediolateral forces were recorded at the handles, the thighs and the feet. Force values at maximal bilateral pushing efforts at each segment and inter-limb coordination between sides were compared. FINDINGS: During the isometric pushes, the paretic maximal forces at the handles for stroke participants were lower than the nonparetic side and lower than both sides of the control participants (p < 0.036). The control and stroke participants had moderate to good coordination for the anteroposterior forces (hands and thighs). While they used similar postural strategies to the controls except for a decreased weight on the paretic foot, vertical forces were less coordinated at the handles and feet in the stroke group (p < 0.050). The inter-trial variability was also higher in the stroke group. INTERPRETATION: Bilateral pushing with gradual efforts induces impaired postural strategies and coordination between limbs in individuals after stroke. It may reveal to be a promising strategy to assess and train post-stroke individuals in a clinical setting. Also, providing feedback would help better control symmetry during efforts.

A method for quantitative evaluation of a valgus knee orthosis using biplane x-ray images.

Knee orthoses are designed to reestablish the normal kinematics of the knee joint. However, the data on the effectiveness of them on modifying the internal joint kinematics are scarce. The aim of this study was to develop a method to allow accurate comparison of the knee contact kinematics in osteoarthritic (OA) subjects with and without wearing a valgus knee orthosis using imaging techniques. Biplane x-ray images of a subject (68 yrs., female, 1.70 m, 89 kg, left knee) was recorded during a weight-bearing squat at five positions. The same squat trial was repeated while wearing the orthosis. The 3D models of the knee were reconstructed from the biplane x-rays and the joint kinematics as well as the tibiofemoral contact point locations and bone-to-bone distance were compared at each posture. This could be seen as a proof of concept for the use of contact point locations as a parameter for evaluating the effectiveness of knee orthoses.Clinical Relevance- Joint kinematics derived from the skin markers suffer from low accuracy. The real impact of the knee orthoses on the skeleton takes vigorous techniques, which allows detecting the subtle kinematics changes directly at the joint level.

Inertial motion capture validation of 3D knee kinematics at various gait speed on the treadmill with a double-pose calibration.

BACKGROUND: Inertial motion capture (IMC) is rapidly gaining in popularity to evaluate gait in clinical settings. Previous examinations of IMC knee kinematics were often limited to the sagittal plane and IMC calibration has not been thoroughly investigated. RESEARCH QUESTION: The objective was to validate IMC 3D knee kinematics calibrated with a double-pose during gait with reference to optical motion capture (OMC). The hypotheses are that IMC can estimate adequately knee kinematics and that both systems will detect similarly the changes with gait speed. METHODS: Twenty-four healthy participants walked on the treadmill at gait speed of 0.6, 0.8, 1.0 and 1.2 m/s. Knee kinematics were obtained simultaneously with two magnetic and inertial measurement units and passive markers fixed on the KneeKG system. OMC was calibrated with a functional anatomical approach and the IMC with a double-pose. RESULTS: Root mean square differences of the two systems yielded 3-6° for knee flexion, adduction and external rotation. Knee kinematics were more similar during the stance phase than the swing phase. Gait speed showed a significant progressive effect on the three knee angles that was similarly detected by the two systems. SIGNIFICANCE: IMC 3D knee kinematics can be obtained independently with a simple calibration and only two magnetic and inertial measurement units at an acceptable level of error especially during stance.

Can a reduction approach predict reliable joint contact and musculo-tendon forces?

Musculoskeletal models generally solve the muscular redundancy by numerical optimisation. They have been extensively validated using instrumented implants. Conversely, a reduction approach considers only one flexor or extensor muscle group at the time to equilibrate the inter-segmental joint moment. It is not clear if such models can still predict reliable joint contact and musculo-tendon forces during gait. Tibiofemoral contact force and gastrocnemii, quadriceps, and hamstrings musculo-tendon forces were estimated using a reduction approach for five subjects walking with an instrumented prosthesis. The errors in the proximal-distal tibiofemoral contact force fell in the range (0.3-0.9 body weight) reported in the literature for musculoskeletal models using numerical optimisation. The musculo-tendon forces were in agreement with the EMG envelops and appeared comparable to the ones reported in the literature with generic musculoskeletal models. Although evident simplifications and limitations, it seems that the reduction approach can provided quite reliable results. It can be a useful pedagogical tool in biomechanics, e.g. to illustrate the theoretical differences between inter-segmental and contact forces, and can provide a first estimate of the joint loadings in subjects with limited musculoskeletal deformities and neurological disorders.

Can total knee arthroplasty restore the correlation between radiographic mechanical axis angle and dynamic coronal plane alignment during gait?

BACKGROUND: Total knee arthroplasty (TKA) is the treatment of choice for end-stage knee osteoarthritis. Postoperative static knee alignment has been recognized as a key component of successful surgery. A correction toward the kinematics of a native knee is expected after TKA, with an aim for neutral mechanical alignment. The evolution of frontal plane knee kinematics is not well understood. METHODS: Nineteen patients awaiting TKA were recruited. Three-dimensional knee kinematics during treadmill gait were assessed pre-operatively, 12 months after surgery, and compared to a control group of 17 asymptomatic participants. RESULTS: Mean radiographic mechanical alignment was corrected from 5.4°â€¯±â€¯5.0 (Standard Deviation) varus pre-operatively to 0.1°â€¯±â€¯2.0 (Standard Deviation) valgus postoperatively (P = 0.002). Mean stance coronal plane alignment decreased from 6.7°â€¯±â€¯4.0 (Standard Deviation) varus per-operatively to 2.1°â€¯±â€¯3.8 (Standard Deviation) postoperatively (P = 0.001). Correlation between radiographic mechanical axis angle and dynamic frontal plane alignment during gait, before and after surgery, was weak (pre-operative R = 0.41; postoperative R = 0.13) compared to control (R = 0.88). In the sagittal plane, TKA patients maintained their pre-operative stiff knee gait adaptation. Postoperative transverse plane kinematics suggested restoration of external tibial rotation during swing after TKA compared to control (Pre-operative 3.1°, postoperative 6.8°, control 7.1°, P = 0.05). CONCLUSION: The lack of correlation between static and dynamic alignment suggests that static radiographic coronal alignment of the knee does not accurately predict dynamic behavior. In the sagittal plane, pre-operative gait adaptations were still present 12 months after surgery, supporting the need for a functional assessment to guide postoperative rehabilitation following TKA.

Activity Monitor Placed at the Nonparetic Ankle Is Accurate in Measuring Step Counts During Community Walking in Poststroke Individuals: A Validation Study.

BACKGROUND: Different environmental factors may affect the accuracy of step-count activity monitors (AM). However, the validation conditions for AM accuracy largely differ from ecological environments. OBJECTIVES: To assess and compare the accuracy of AM in counting steps among poststroke individuals: during different locomotor tasks, with AM placed at the nonparetic ankle or hip, and when walking in a laboratory or inside a mall. DESIGN: Validation study. SETTINGS: Laboratory and community settings. PARTICIPANTS: Twenty persons with chronic hemiparesis, independent walkers. METHODS: First session: participants performed level walking (6-minute walk test [6MWT]), ramps, and stairs in the laboratory with AM placed at the nonparetic ankle and hip. Second session: participants walked a mall circuit, including the three tasks, with AM placed at the nonparetic ankle. The sessions were video recorded. MAIN OUTCOME MEASUREMENTS: Absolute difference between the steps counted by AM and the steps viewed on the video recordings (errors, %); occurrence of errors greater than 10%. RESULTS: Median errors were similar for the 6MWT (0.86 [0.22, 7.70]%), ramps (2.17 [0.89, 9.61]%), and stairs (8.33 [2.65, 19.22]%) with AM at the ankle. Step-count error was lower when AM was placed at the ankle (8.33 [2.65, 19.22]%) than at the hip (9.26 [3.25, 42.63]%, P = .03). The greatest errors were observed among the slowest participants (≤0.4 m/s) on ramps and stairs, whereas some faster participants (>1 m/s) experienced the greatest error during the 6MWT. Median error was slightly increased in the mall circuit (2.67 [0.61, 12.54]%) compared with the 6MWT (0.50 [0.24, 6.79]%, P = .04), with more participants showing errors >10% during the circuit (7 vs 2, P = .05). CONCLUSIONS: Step counts are accurately measured with AM placed at the nonparetic ankle in laboratory and community settings. Accuracy can be altered by stairs and ramps among the slowest walkers and by prolonged walking tasks among faster walkers. LEVEL OF EVIDENCE: III.

Stroke pattern classification during manual wheelchair propulsion in the elderly using fuzzy clustering.

The purpose of this study was to analyse the kinematic pattern of elderly group during manual wheelchair propulsion. Fourteen elderly persons propelled manually in a wheelchair ergometer. A new objective method based on metrical and topological aspect of the contour of hand center of mass is proposed. A geometric mapping transforms the original time-hand trajectory to a normalized couple of features (R1 and R2). Fuzzy clustering was used to classify wheelchair propulsion pattern based on their features R1 and R2. Four classes were found in order to represent different propulsion pattern. Significant differences were found between classes for fraction of effective force and the biomechanical effectiveness. It was also found that classes are posture dependent and this can help in developing rehabilitation programmes for different groups of patients.

The effect of resultant force at the pushrim on shoulder kinetics during manual wheelchair propulsion: a simulation study.

The aim of this study was to determine, by simulation on real data, the effect of modifying the direction or effectiveness of a given force amplitude on the load sustained by the shoulder estimated by joint forces and moments. Kinematics and kinetics data were recorded on 14 manual wheelchair users 68.2+/-5.2 years for 10 s at sub-maximal speed (0.96-1.01 m/s). The simulation consisted in modifying force effectiveness at the pushrim while maintaining the same initial force amplitude. Shoulder kinetics were computed for simulated resultant forces from radial to tangent directions and also for initial force effectiveness. The results show that as the force was simulated tangent to the wheel, there was a significant increase in the average proximal and anterior shoulder joint forces. Also, significant increases in average internal rotation, flexion in the sagittal and horizontal plane moments were reported. Higher shoulder kinetics could accelerate the onset of fatigue and increase the risk of injury. A single-case analysis revealed an improvement window for force effectiveness ( approximately 10%) in which shoulder kinetics were not substantially increased. Our results provide useful information on what would happen to shoulder kinetics if we were able to teach manual wheelchair users to modify their force pattern at the pushrim. The results suggest that for an elderly population, it is not wise to aim at producing a mechanically optimal resultant force at the pushrim (i.e., tangent). Smaller increases of the initial force effectiveness would be preferable.

Automatic classification of asymptomatic and osteoarthritis knee gait patterns using kinematic data features and the nearest neighbor classifier.

The aim of this work is to develop an automatic computer method to distinguish between asymptomatic (AS) and osteoarthritis (OA) knee gait patterns using 3-D ground reaction force (GRF) measurements. GRF features are first extracted from the force vector variations as a function of time and then classified by the nearest neighbor rule. We investigated two different features: the coefficients of a polynomial expansion and the coefficients of a wavelet decomposition. We also analyzed the impact of each GRF component (vertical, anteroposterior, and medial lateral) on classification. The best discrimination rate (91%) was achieved with the wavelet decomposition using the anteroposterior and the medial lateral components. These results demonstrate the validity of the representation and the classifier for automatic classification of AS and OA knee gait patterns. They also highlight the relevance of the anteroposterior and medial lateral force components in gait pattern classification.

New accelerometric method to discriminate between asymptomatic subjects and patients with medial knee osteoarthritis during 3-d gait.

This study presents a new method to estimate 3-D linear accelerations at tibial and femoral functional coordinate systems. The method combines the use of 3-D accelerometers, 3-D gyroscopes and reflective markers rigidly fixed on an exoskeleton and, a functional postural calibration method. Marker positions were tracked by a six-camera optoelectronic system (VICON 460, Oxford Metrics). The purpose of this study was to determine if this method could discriminate between medial osteoarthritic and asymptomatic knees during gait. Nine patients with osteoarthritic knees and nine asymptomatic control subjects were included in this study. Eighteen parameters representing maximal, minimal, and range of acceleration values were extracted during the loading and preswing to mid-swing phase periods, and were compared in both groups. Results show good discriminative capacity of the new method. Eight parameters were significantly different between both groups. The proposed method has the potential to be used in comprehending and monitoring gait strategy in patients with osteoarthritic knee.

Relationship between resultant force at the pushrim and the net shoulder joint moments during manual wheelchair propulsion in elderly persons.

OBJECTIVE: To determine the relationship between the resultant force at the pushrim and the net shoulder joint moments during manual wheelchair propulsion in elderly persons. DESIGN: Convenience sample. SETTING: Motion analysis laboratory. PARTICIPANTS: Older manual wheelchair users (N=14; age, 68.2+/-5.2y) were tested. INTERVENTIONS: Kinematic and kinetic data were collected during manual wheelchair propulsion at a speed between 0.96 and 1.01m/s for 10 seconds and at a power output around 22.4W on a wheelchair ergometer. MAIN OUTCOME MEASURES: Net shoulder joint moments were computed with an inverse dynamic model. The mechanical use of the forces at the pushrim and the mechanical fraction of effective force were measured during propulsion. RESULTS: Mechanical use and mechanical fraction of effective force had a positive and significant correlation with the net internal (P<.05) and external (P<.001) shoulder rotation moment, the net flexion (P<.05), and extension (P<.001) moment in the sagittal plane, and the net flexion (P<.001) moment in the horizontal plane. CONCLUSIONS: The results suggest that because the resultant force at the pushrim has a greater tangential component and a greater proportion of the maximal voluntary force, most of the net moments around the shoulder are higher. Thus the optimal way of propelling, from a mechanical point of view (ie, tangential), may not be advantageous for manual wheelchair users.

Test-retest reliability and minimal clinical change determination for 3-dimensional tibial and femoral accelerations during treadmill walking in knee osteoarthritis patients.

OBJECTIVE: To determine the test-retest reliability and the minimal clinical change determination for accelerometric parameters, estimated by a new accelerometric-based method that estimates 3-dimensional (3D) linear accelerations of the tibia and femur during comfortable and fast walking speeds. DESIGN: Test-retest study. SETTING: Gait laboratory in a research center. PARTICIPANTS: Patients (N=25; 6 men, 19 women) with symptomatic knee osteoarthritis (OA). INTERVENTIONS: Not applicable. MAIN OUTCOMES MEASURES: Subjects attended 2 walking sessions in which accelerometers were rigidly fixed by means of an exoskeleton to the femoral and tibial segments. In both sessions, 3D accelerations were collected for 25 seconds for each of the walking speeds. Mean accelerometric pattern was calculated using 15 gait cycles. From each mean pattern, maximal, minimal, and range values were extracted from the loading phase period. The root mean square (RMS) value was also calculated for every pattern. Relative and absolute reliability were determined using intraclass correlation (ICC) and standard error (SE) of measurement, respectively. Minimal detectable change was calculated for each parameter as the least significant difference. RESULTS: Tibial and femoral accelerations showed reliable values across sessions 1 and 2 with ICCs greater than or equal to .75 for 96% and 88% of the parameters at comfortable and fast speeds, respectively. The SE of measurement ranged from .01 to .05g for the RMS value and from .05 to .35g for maximal, minimum, and range point parameters. CONCLUSIONS: The proposed method is the first to have determined the reliability and the minimal detectable change for tibial and femoral acceleration parameters in knee OA patients during a treadmill walking evaluation. The minimal detectable change determined in this study will be used to determine improvement or deterioration of knee OA patients after rehabilitation.